Edge coating



March 12, 1963 H. G. CHINN 3,081,213

EDGE comm:

Original Filed May 2, 1958 Roll of Coar ed Paper 2 Sheets-Shoot lCoa'red Cpmainer 24 lnierlor 3 K 44 i'i'fii 30 OutsIde of INVENTOR.HARRY G. CHINN ATTORNEY March 12, 1963 H. G. CHlNN 3,081, 3

EDGE COATING Original Filed May' 2, 1958 2 Sheets-Sheet 2 Hoi Resin u' I34 8 a /5 IIIIWHH i- Coared INVENTOR.

Edge HARRY G. CHINN 2H "JIM;

A T TORNEY United States 3,081,213 EDGE COATING Harry G. Chinn,Somerville, N.J., assignor to Union Carbide Corporation, a corporationof New York Original application May 2, 1958, Ser. No. 732,544 Dividedand this application Apr. 13, 1960, Ser. No.

2 Claims. or. 156-192) atent ever increasing use in the packaging ofcomestibles, hardware items, machine parts, chemicals and divers othercommodities. fabricated from paper, cardboard, fabrics made of naturalor synthetic fibers, metal foil and other sheet-like materials whichhave been coated with, laminated to, or otherwise surfaced, on one orboth sides, with a film of the thermoplastic resin composition, or frommore complex, resin coated, multJi-ply, laminated, sheet-likestructures.

An uninterrupted, continuous resin film serves as an inert, chemicallyresistant, moisture and vapor impermeable barrier which protects thesheet-like material from the packaged material, and simultaneously,guards the package contents from contamination by the sheet material andagainst spoilage by atmospheric or other external agents. However, thereis almost invariably present in such containers-and in many otherarticles fabricated from resin coated sheets, such as rainwear and thelikeone or more sheet edges which, since they are uncoated, represent adiscontinuity in the resin layer and permit the package contents to comeinto contact with the sheet material and the external environment,sometimes allow leakage from the package, frequently destroy thecompletely moistureproof nature of the container, and otherwise preventthe resin coating from fulfilling its proper function. These edgeeffects are particularly severe when the contents of the package areliquids or foodstuffs or the like, and frequently render such packagesunacceptable for said type materials.

It is, therefore, the main object of the present invention to coat suchedge with a thermoplastic resin composition, particularly with apolyethylene resin composition.

According to the present invention, a substantially U- or V-shapedcoating of hot thermoplastic materials is extruded onto at least oneuncoated edge of sheet material.

The method is extremely versatile in that the coating material can be ofany extrudable composition, such as polyethylenic or vinyl resincompositions or the like. Such an edge coating can be applied tovirtually any sheetlike material of either single-ply or multi-plyconstruction and regardless. of its thickness, as for example, paper,metal foil, coated paper, resin coated laminates, etc. The thickness ofthe coating and the width of the edge-abutting, sheet-surface marginswhich are coated can be predetermined and controlled. Additionaladvantages will become apparent from the following consideration ofcertain specific applications wherein the novel, edge coated webs ofthis invention are particularly useful.

The long seal of a bag made from plastic coated paper is, in itsstrongest form, an overlap seal. There is normally present inside of aso-sealed bag, an uncoated edge of paper which runs the full length ofthe bag. Furthermore, a very large volume of bags are fabricated Suchcontainers are most economically from paper coated on one side only, saywith polyethylene;

ice

Hence a polyethylene-to-paper bond must be effected to make the seal. Byedge coating the plastic coated paper by the method of this invention,the interior raw edge is eliminated and the seal is formed by effectinga plastic-toplastic bond which is much more easily and more reliablyaccomplished than a plastic-to-paper bond.

Further, if such bags are used to contain liquid, the raw edge of thepaper acts as a wick, which is undesirable both per se and because itinduces staining which renders the container unsightly. Moreover,materials eluted from the paper fibers can sometimes contaminate thecontents of the package during long storage periods.

Similar benefits are apparent in coated boxboard containers, convoluteand spirally wound tubular containers, and the like. In such cases, theuse of a sheet which has been edge coated by the instant method providesa completely continuous plastic coating on the inside ofthe container,and simultaneously, provides plastic-to-plastic surfaces for bonding.Furthermore, the edge coating process lends itself to the simultaneoussealing of these seams in the container manufacturing process; and saidsealing operation requires no apparatus or adhesive other than the dieand hot melt used to edge coat the web.

In the drawings:

FIG. 1 is a diagrammatic isometric view of apparatus according to, andfor carrying out the method of, the preferred embodiment of the presentinvention;

FIG. 2 is a section taken along the line 2-2 of FIG. 1;

FIG. 3 is a pictorial view of the preferred embodiment of a product;

FIG. 4 is a section taken along the line 4--4 of FIG. 3

FIG. 5 is an exploded view of the die shown in FIG. 1;

FIG. 6 is an assembled view of the die shown in FIG. 5;

FIG. 7 is a vertical section taken along the line 77 of FIG. 6; and

FIG. 8 is a horizontal section taken along the line 88 of FIG. 7.

The edge-coating die described hereinafter may be installed on aconventional extruder. It may then be so used; or in conjunction with asingle roll over which the edge-coated web is passed in tension; orinconjunction with a pair of pressure rolls in an arrangement such asdescribed in the copending application of W. A. Haine and myself, SerialNo. 594,929, filed November 29, 1956, i.e., by substituting said die forthe bead sealing die. In other words, the extruded edge coating may beadhered adequately to the web merely by extrusion thereonto, or byextruding and subsequently urging said extruded coating against one oragainst both surfaces of the web, respectively.

In the preferred embodiment, the extrusion die consists of a shell and aguide mounted in the shell in such manner as to provide between theshell and the guide a chamber for hot resin. A resin feed or inlet tubedelivers the hot resin from the extruder into the die chamber.

As shown in FIG. 1, sheet material 10 which has been coated on one sidewith thermoplastic composition 12 but has an exposed or uncoated edge14, is withdrawn from a supply roll 16 and passed through an edgecoating die 18. Hot thermoplastic material is supplied to the die 18from an extruder (not shown) through die inlet tube 20.

The die 18 extrudes a shaped coating 22 of hot thermoplastic materialonto the uncoated edge 14 and fused thereto, and overlapping theadjacent surfaces of the sheet material 10 and fused thereto. Thecoating 22 is preferably shaped like a beam section such as an angle orchannel, so that the portion 23 thereof engaging the exposed edge 14 maybe the apex portion of an angle or the web of a channel. The portions 24and as overlapping the adjacent sheet surfaces are the legs or flangesof such angle or channel, respectively.

The entire coating including the crown portion and both leg or flangeportions, is firmly adhered to the sheet at the sheet edge and at thesheet margins adjacent thereto. If one or both sheet surfaces is coated,for example, with thermoplastic, then the mating portions of suchcoating and of the edge coating are actually fused together.

As shown in FIG 5, the die 18 comprises an outer casing consistingconveniently of a top shell 30 and a bottom shell 32, and a sheet guidecore 34 having a slot 36 through which the sheet 10 passes. The shells30 and 32 have complementary registering cavities 38 and 40, and thecore 34 has a substantially conical outer surface 42 forming with thecavities 38 and 40 a hot resin chamber.

As shown in PEG. 8, the conical surface 42 terminates short of the frontof the cavities 38 and 40, so that the hot resin from the hot resinchamber contacts the edge and both sides of the sheet 10. As shown inFIG. 5, the shells 38 and 40 have registering grooves 44 and 46 formingan extrusion slot the dimensions of which partially determine thedimensions of the applied edge coating 22.

The edge-coating die described above was installed, with its guide slitdisposed horizontally in the molten bead sealer apparatus described inthe aforesaid copending application, in place of the bead sealing die. Aroll of mil thick kraft paper carrying a one mil thick coating ofpolyethylene on one side was placed on the machine. Some runs were madewith the plastic coating facing down and others with the plastic coatingfacing up, both with equally good results. Prior to starting theextruder screw, the extruder barrel was heated to the temperaturerequired to provide a free flowing resin melt. This compound temperaturedepends on the particular resin composition employed. For polyethyleniccompositions, temperatures between about 200 C. and about 300 C.generally give the best results. In this particular run, the rear andmiddle sections of the extruder barrel were maintained at 1.00 and 250C., respectively, and the front section of the barrel and the die weremaintained at 300 C. The resin employed was a commercial polyethyleneresin having a melt index of 2 and a density of 0.918 g./cc. at 23 C.(Bakelite Companys DYNH 3).

The paper was then threaded through the die slit and drawn through atspeeds ranging from about 50 to 70 feet per minute, at which web speedsthe resin extrusion rate ranged from about 3.5 to 4 pounds per hour. Theresin flow rate was adjusted to the speed of the paper until a thincoating of hot melt was placed on both sides of the paper and over theedge. On the coated side of the paper, a /2 inch wide by 3.25 mil thickskirt blended evenly with the original coating; and on the uncoated sideof the paper, a /2 inch wide by 3.25 mil thick coating of polyethylene,which was strongly adhered to the surface of the paper, was laid ontothe edge portion of said paper surface.

On examination of the samples produced, it was observed that the edge ofthe newly made coating protruded slightly beyond the edge of the paper.It was found that this overlap could be increased or decreased asdesired by respectively increasing or decreasing the resin flow raterelative to the paper speed through the die, whereby, in effect, thethickness of the crown portion of the edge coating was adjustable.

At the process speeds quoted above, sufficient heat remained in theso-applied edge coating to form strong bonds with other coated samplesas far as 30 inches from the die.

The samples cited above were made with air cooling only; but watercooled rollers can be used, if desired, to set the hot melt in shorterdistances.

When the edge-coated sheet so formed was spirally wound into a containerwith the coating 12 inside, as shown in FIG. 3, the coating flange 26overlying and fused to the uncoated outer surface of the sheet 10 wasfirmly fused to the coating 12 of the next convolution of the sheet 10thereover, as shown in FIG. 4, to provide the container with acontinuous thermoplastic inner surface.

What is claimed is:

1. Method of forming a strong, moisture-proof bond between margins ofsheet material coated on at least one side with thermoplastic resincomposition, which comprises continuously sealing an edge of paper-thin,smoothsurfaced, dense homogeneous sheet material by continuouslywithdrawing said material from a supply roll and passing it along arectilinear path, continuously extruding a hollow mass of hotthermoplastic resin material having an interior converging in thedirection of said path and channel shaped in cross section with upperand lower flats and a connecting web, continuously directing said webonto said edge and said flats onto said sheet surface margins adjacentsaid edge at a point in said rectilinear path and continuously adheringsaid coating to said edge and said margins as they pass beyond saidpoint and on along said rectilinear path, and progressively applyingsaid edge-coated margin over another surface coated margin inoverlapping relation therewith while sufiicient heat remains in saidedge coated margin to form strong bonds to fuse the edge coating of thefirst margin to the surface coating of the second.

2. A method of forming a strong, moisture-proof bond between margins ofsheet material coated on at least one surface with a thermoplastic resincomposition, which comprises continuously extruding a hollow mass of hotthermoplastic resin material having an interior converging toward saidsheet material and angle shaped in cross section with a fiat and aflange connected thereto, continuously directing said flat onto one edgeand the flange onto the uncoated margin adjacent said edge, and spirallywinding said sheet with the coating inside and the coating flangeoverlying and fused to the uncoated outer surface of said sheet, andfusing said flange to the coating of the next convolution of the sheet.

References Cited in the file of this patent UNITED STATES PATENTS2,115,368 Tustberg Apr. 26, 1938 2,138,699 Hinze Nov. 29, 1938 2,293,252Foster Aug. 18, 1942 2,354,426 Briant July 25, 1944 2,415,721 Arner Feb.11, 1947 2,550,520 Bennett Apr. 24, 1951 2,555,380 Stuart June 5, 19512,623,444 Maier Dec. 30, 1952 2,677,633 Gross May 4, 1954 2,748,044Seiler May 29, 1956 2,757,709 Crabbe Aug. 7, 1956 2,786,622 Ross Mar.26, 1957 2,821,497 Works Jan. 28, 1958 2,874,752 Brey Feb. 24, 1959

1. METHOD OF FORMING A STRONG, MOISTURE-PROOF BOND BETWEEN MARGINS OFSHEET MATERIAL COATED ON AT LEAST ONE SIDE WITH THERMOPLASTIC RESINCOMPOSITION, WHICH COMPRISES CONTINUOUSLY SEALING AN EDGE OF PAPER-THIN,SMOOTHSURFACED, DENSE HOMOGENEOUS SHEET MATERIAL BY CONTINUOUSLYWITHDRAWING SAID MATERIAL FROM A SUPPLY ROLL AND PASSING IT ALONG ARECTILINEAR PATH, CONTINUOUSLY EXTRUDING A HOLLOW MASS OF HOTTHERMOPLASTIC RESIN MATERIAL HAING AN INTERIOR CONVERGING IN THEDIRECTION OF SAID PATH AND CHANNEL SHAPED IN CROSS SECTION WITH UPPERAND LOWER FLATS AND A CONNECTING WEB, CONTINUOUSLY DIRECTING SAID WEBONTO SAID EDGE AND SAID FLATS ONTO SAID SHEET SURFACE MARGINS ADJACENTSAID EDGE AT A POINT IN SAID SURFACE PATH AND CONTINOUSLY ADHERING SAIDCOATING TO SAID EDGE AND SAID MARGINS AS THEY PASS BEYOND SAID POINT ANDON ALONG SAD RECTILINEAR PATH, AND PROGRESSIVELY APPLYING SAIDEDGE-COATED MARGIN OVER ANOTHER SURFACE COATED MARGIN IN OVERLAPPINGRELATION THEREWITH WHILE SUFFICIENT HEAT REMAINS IN SAID EDGE COATEDMARGIN TO FORM STRONG BONDS TO FUSE THE EDGE COATING OF THE FIRST MARGINTO THE SURFACE COATING OF THE SECOND.